The present invention relates to a friction damped mechanical tensioning device for belt or chain drives, commonly referred to tension element drives, which are commonly used on internal combustion engines.
Mechanical tensioners are used to automatically control the tension of a tension element, such as a belt or chain, on the accessory drive typically located at the front of internal combustion engines used in automobiles as well as other motor driven equipment. Known tensioners, such as shown in FIGS. 2A-2E, typically include a pivoting arm having a tension pulley located at its distal end. The arm is rotatable about a pivot axis provided by a mounting base, and is biased via a torsion spring, usually mounted about the pivot axis, with one end connected to the pivot arm and the other end attached to the base to bias the tension pulley located on the arm against a tension element drive. In many known arrangements, such as shown in FIGS. 2B-2E, the spring generates an additional axial force so that a portion of the pivot arm adjacent to the pivot axis is pressed against a damping element to control oscillatory movements of the pivot arm.
As shown in FIGS. 2A-2E, in the prior art devices, the tension pulley is generally offset in relation to the pivot bushing or bearing which rotatably supports the pivot arm, and this bushing or bearing must carry offset loads due to the moment generated by the offset between the tension pulley and the bushing or bearing arrangement in the mounting base. This results in uneven or excessive wear of the bushing along with the attendant pulling of the pivot arm out of its desired alignment. Further, this compromises the damping ability of the tensioner based on uneven wear, particularly with disk-type damping elements which wear unevenly in the radial direction. Cone dampers also wear unevenly in the radial direction, and damping shoes require a more complex design due to uneven bushing wear.